1. Field of the Invention
The present invention relates to the manufacture of high temperature resistant materials, and more particularly to a pliable, nonwoven tape suitable for use in the protection of missile nose cones, leading edges and the like.
In missiles, or for that matter, for any item to be subjected to high heating rates, a number of schemes have been devised for protecting the surface areas from the effects of high temperature. Of these, perhaps ablative materials which absorb the heat energy by vaporization, sublimation or by melting of a surface coating material to protect the missile and its instrumentation are the most commonly used. However, fluid cooling, in which a fluid absorbs the heat energy by a rise in the temperature of the fluid used; heat sinks of a nonmelting shielding material; and transpiraton cooling in which a vapor or gas is diffused through a porous skin onto the heated surface have also been suggested. The present invention deals with a novel ablative type material for a missile nose cone or the like, but it obviously may be used in many other utilizations where intense heating is to be experienced.
In nose cone technology, the temperature limitation involved in the proper protection of the structural shell and the components of the payload inside the shell is a most important factor. The most desirable ablative material is one with a high heat of ablation and a low thermal conductivity. However, various materials possess one or the other characteristic in different degrees and in addition, many of the materials that possess other desirable properties do not have the necessary structural strength. Materials must be selected on the basis of the minimum weight required to maintain the temperature within the design limits, and ablative materials must be matched to the environment in which they are to be used. For example, many materials rapidly deteriorate without ablating if exposed for a length of time to temperature below their ablation temperatures and thus will not provide protection for the structure when most needed. Commonly used ablative materials include quartz, graphite and teflon.
2. Description of the Prior Art
The majority of prior art ablative constructions used in missile nose cones have been made by a shingle wrap method in which a woven fiberglass or silica material is impregnated with a phenolic resin and wrapped upon the structure with a shingle type overlap. The resin in the impregnated fiberglass or silica is then cured by heating under controlled conditions. This type of ablator, however, tends to become irregular when the cured resin ablates away, and the exposed reinforcing fibers tend to melt out or come loose. It has been suggested to provide a fiberglass woven rug impregnated with a resin whereby the woven fibers may be placed normal to the exterior surface of the nose cone rather than parallel to the surface. This placing of the fibers perpendicular to the surface prevents the material ablating in an irregular manner and prevents the fibers from washing out of matrix as ablation takes place. However, it has been found that construction of fiberglass or other material. woven in a rug-like manner and then impregnated with a resin and cured, is not an arrangement in which the reinforcing fibers can become thick or close-packed together for best operation, and does not allow sufficient freedom in aligning the fibers at preferred angles on the surface to which it is being applied.
Other ablative constructions include cast resins without fiber reinforcement or reinforcement with various materials such as honeycomb core. One suggested solution to the rapid heating problems encountered in nose cones involves the anchoring of a fiber pile to the surface of a nose cone with unimpregnated fibers protruding out of the anchoring base of epoxy resin or the like.